The biocompatibility screening of the biomaterials used in dentistry is essential to protect patients from avoidable health risks;allergic reactions, treatment failure, tissue injury, pain and suffering, disability, disfigurement, reduction in quality of life, and serious adverse health events. The biocompatibility screening standard set by the American National Standards Institute/American Dental Association (ANSI/ADA) Document No. 41a, and the biocompatibility screening guidelines (7405 and 10933) set by the International Organization for Standardization (ISO) has advocated the same tests since the 1950s. The regulatory agencies responsible for protecting patients from potential health hazards require that the biocompatibility screening assays be updated to modern biological standards. Congruent with ANSI/ADA/ISO recommendations, our central hypothesis is to safeguard patients from potential health risks by developing new biocompatibility assays with an improved clinical relevance. The objective of this particular application is to create highly reproducible and economical in vitro biocompatibility screening assays to be incorporated in future ANSI/ADA/ISO guidelines as an alternative to many animal experiments and clinical trials. We have assembled a histological archive of 30,000 in situ restored human teeth that will be used to assess the clinical relevance of the in vitro biocompatibility screening assays specified by the American National Standards Institute/American Dental Association (ANSI/ADA), and the biocompatibility screening guidelines (ISO 7405 and 10933). Guided by strong preliminary data, our rationale will be tested by pursuing four specific aims: 1) Test the hypothesis that ANSI/ADA/ISO recommended biocompatibility screening assays have little clinical relevance. 2) Test the hypothesis that tooth organ culture biocompatibility assays have a greater clinical translational relevance than the ANSI/ADA/ISO recommended biocompatibility screening assays. 3) Test the hypothesis that tooth organ-culture assays are a stable method for the biocompatibility screening of tissue engineering materials. 4) Test the hypothesis that heat shock protein expression in tooth organ culture can provide more clinically-relevant tissue-injury information than current ANSI/ADA/ISO in vitro biocompatibility screening assay endpoints. The outcomes of this research will be quicker, more cost-effective, and more clinically relevant biocompatibility screening assays that will reduce the need for animal experimentation, and increase the safety of participants in clinical trials. The proposed research is significant, because biomaterials are being used in the 290 million dental treatments provided to American patients each year.